88
votes
Accepted
Why does Io cast a hard shadow on Jupiter, but the Moon casts a soft shadow on Earth?
It's due to the larger relative apparent size of the Sun. When the source of light is a point source the shadow is harder, and when it is extended it is softer.
Jupiter is approximately 5 times more ...
- 3,140
46
votes
Accepted
Counting from the 21st century forward, what place on Earth will be last to experience a total solar eclipse?
Here is a combination of the maps available from NASA SEAtlas. They cover time span from year 2001 to 3000. Made with a custom Python script and some editing in GIMP.
The yellow to blue colors mark ...
- 1,600
40
votes
Is it possible that the shadow of The Moon is a single dot during solar eclipse?
What you are calling a focal point is the end of the umbra, the point at which the umbra changes to the antumbra. In a total solar eclipse, that point is below rather than above the surface of the ...
- 33.5k
39
votes
Can a planet in our system eclipse the sun as seen from another one?
In our solar system, it is possible for one planet to partially eclipse the sun, but it is not possible for any planet to cause a full solar eclipse as seen from another planet.
The sun is too big and ...
- 16.2k
34
votes
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Will just a glimpse (less than a second) of sun during partial solar eclipse damage eyes?
Glancing at a partial solar eclipse is about as dangerous as glancing at the Sun on any other day. If you look at the Sun a few minutes after sunrise or a few minutes before sunset, when the Sun's ...
- 13.1k
32
votes
Why does Io cast a hard shadow on Jupiter, but the Moon casts a soft shadow on Earth?
Due to the basic proportionality theorem, the width of the boundary of the shadow is
$$
w=\frac{\ell D}L\;,
$$
where $\ell$ is the distance from the moon to the planet’s surface, $L$ is the ...
- 421
30
votes
Is it possible to see mercury transit "clearly" by the naked eye?
I did see the Venus transit before the Sun in 2004.
I used no telescope, but of course I used proper solar eclipse glasses to protect my eyes. The black circle was small but clearly visible.
But ...
- 415
28
votes
Why is it okay to watch a sunset but not an eclipse?
During a sunset, the Sun is lower in the sky than during most of the day - much lower. Therefore, light from the Sun travels through about 120 miles of dense atmosphere, compared to the roughly 2 ...
- 36k
27
votes
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Is it possible to see mercury transit "clearly" by the naked eye?
I'll use the atmosphere as my big natural lens. So I'll watch the upcoming mercury transit at the sunset time where the sun looks bigger than usual.
While the Sun and Moon might seem larger at the ...
- 31.4k
23
votes
Accepted
Was the Sun's gravitational lensing observed in other solar eclipses than the one in 1919?
Yes, observations of this kind are within the technical scope of amateur astronomers. Several groups succeeded in replicating the experiment during the 2017 eclipse that crossed the USA.
For example ...
- 116k
23
votes
During an eclipse, how big is the shadow of the moon on the earth?
But how big is this shadow? How many kilometers is its diameter?
That's a photo of the umbra and penumbra on the surface of the Earth taken from Space. It's a little distorted because it's not ...
- 31.4k
22
votes
Can a planet in our system eclipse the sun as seen from another one?
The short answer is no. The alignment occurs, but the eclipse does not, due to the distances and size differences involved.
There are a few things to consider here. You already mentioned a lot of them,...
- 381
20
votes
Accepted
Orbit of the moon so that there are no eclipses
Answer: yes, a no-eclipse orbit is possible
The plane of the Earth-Sun orbit (the ecliptic) and the plane of the Earth-Moon orbit must intersect each other because they both contain at least one point ...
- 930
19
votes
Accepted
During an eclipse, how big is the shadow of the moon on the earth?
The umbra has a well defined diameter but the size varies due to the eccentricity of the orbits of the Earth and of the Moon. The Moon may be so far away that it can't fill the solar disk at all (for ...
- 398
19
votes
Accepted
During a total solar eclipse is it possible to see solar flares with the naked eye?
If by 'solar flare' you mean a coronal mass ejection, then yes, in theory you could see one during a total eclipse if there happened to be one that was at approximately 90 degrees to Earth at the time ...
- 2,023
18
votes
Apparently two objects in Solar Eclipse image
The people who say it is an internal reflection are right. This is an internal reflection inside the lens of the camera. There is no actual object there. In particular, Venus is not visible this ...
- 116k
18
votes
Accepted
Apparently two objects in Solar Eclipse image
It's an internal reflection. The dead giveaway is that in the second picture, the reflected image is a point reflection at the center of the image optical axis (assuming the image was not cropped).
...
- 729
17
votes
Counting from the 21st century forward, what place on Earth will be last to experience a total solar eclipse?
Short answer is that no one knows, there's too much margin for error.
There is too much margin for error, just in the Earth's rotation. The Earth does not rotate at a constant rate, partly due to the ...
- 5,562
16
votes
Why can't we see a solar eclipse every month?
The Moon orbits in a plane that is inclined with respect to the plane in which the Earth orbits. The intersection between these two planes is a straight line. For an eclipse to occur, this straight ...
- 17.4k
15
votes
Is it possible that the shadow of The Moon is a single dot during solar eclipse?
As the Moon's eccentric orbit around the Earth brings it nearer and farther, current solar eclipses can be total or annular.
A few in between are
hybrid eclipses: total along the midday part of the ...
- 18.2k
13
votes
Why does Io cast a hard shadow on Jupiter, but the Moon casts a soft shadow on Earth?
Another factor is involved in addition to the above answers.
Io's umbral shadow is a bit over two million kilometers long, almost six times longer than the ~350 thousand kilometer distance between ...
- 33.5k
13
votes
Will just a glimpse (less than a second) of sun during partial solar eclipse damage eyes?
This webpage gives a lot of background information. Key points:
It does seem to be the overall dimness of near-total eclipses that allows the pupil to widen enough to allow damaging levels of UV in.
...
- 3,691
12
votes
Apparently two objects in Solar Eclipse image
I used the same lens flare effect (internal reflections from the camera's optical surfaces) to image the eclipse from my phone. The shape (as well as the location) was a symmetric reflection about the ...
- 31.4k
12
votes
Accepted
Could there be an eclipse tomorrow if the Pleiades is covered by the Moon tonight?
Consider how far the pleiades are above the ecliptic, and how far the moon travels in a day. From this you can work the angle at which the moon must travel relative to the ecliptic, in order to cross ...
- 4,304
11
votes
Accepted
Dark enough to see stars during total solar eclipse?
One thing to double check is if you can see stars easily at night from the same location. If there are city lights nearby, combined with humidity or dust you can have a bright sky due to terrestrial ...
- 31.4k
11
votes
Is it possible to block the surrounding light in a solar eclipse if we made the moon bigger or closer to the earth?
Let's clarify what "ring of light" you want to cover. In the original photo, the bright spot is the photosphere ("P" in the annotated copy or the original image). The photosphere ...
- 7,797
10
votes
Accepted
What does a solar eclipse at 99% totality look like?
At 99% the Sun will be reduced to a small sliver. There are simulations on the internet. It will become notably darker. However, the Sun is 400,000 times brighter than the full moon, so 1% of the Sun ...
- 116k
10
votes
Why aren't there eclipses every month when the moon's orbit is aligned with the ecliptic as a result of lunar precession?
There are few things here I think might be worth to state:
The tilt of Earth is of no importance here. As the comment says what is of importance how much the Moon orbit is inclined to the ecliptic. ...
- 1,667
10
votes
Accepted
How close is a typical New Moon to the Sun in the sky?
Mean angular separation of about 3.2°, based on skyfield Python library simulation of the 2nd millennium.
This is pretty dependent on your viewing location. The ...
- 4,695
10
votes
During a total solar eclipse is it possible to see solar flares with the naked eye?
There are flares and then there are prominences These are rather different things.
A solar flare is a sudden release of energy from the surface of the sun (including a lot of X-rays). A prominence is ...
- 116k
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